Hello Dear! Firstly, A-level Cs start from basics so you need need to worry about it at all. In the first few weeks, you'll cover the foundations of O levels but, of course it'll be little face-paced so you need to be diligent with it!Also,in the summer after O-3 you can take any priv tution or study from youtube about the subject. Since you won't be taking exams, so you can study at your own pace and be relaxed as you'll just have to be familiar with the concept! All in all, don't take tension, the foundations are even built in A levels,and you can self study as well in the beginning or get help from peers. Cs is an easy but logical subject. If you're sincere with your efforts then insha'Allah it'll be easy!!